Audio content digital watermark detection

ABSTRACT

Digital watermark detection apparatus including detection units which calculate detected values of watermark signals by use of keys for PCM data of channels of audio content, a plurality of units which add the detected values corresponding to each of the channels and each of the keys for each possible combination of the respective channels and the respective keys, and a unit which selects and outputs one adding result from the respective adding results by the plurality of detected value adding units. Moreover, it includes units which accumulate the detected values in accumulation cycles different from one another to restore messages embedded as digital watermarks from the accumulated detected values, and perform boundary detection of the audio contents to detect the audio contents in which the digital watermarks are embedded, and a detection result output unit which synthesizes and outputs respective processing results by the message restoration units.

FIELD OF THE INVENTION

The present invention relates to embedding and detection of a digitalwatermark for audio content, and particularly to an embedding method anddetection method of a digital watermark high in robustness todeterioration of the content.

BACKGROUND OF THE INVENTION

Nowadays, as means for preventing secondary use of audio contentsconverted into digital data, such as illicit copy and modificationthereof, a digital watermark technology for embedding specificinformation in the audio contents is widely utilized.

In the digital watermark technology, the same information (watermarkinformation) is repeatedly embedded in a plurality of spots of apiece ofaudio content. Then, when detecting the watermark information, valuesdetected from the respective spots embedding the watermark informationare accumulated in a buffer, intensified together, and then subjected toprocessing such as error correction. Thereafter, a detection result isoutputted.

As a general technique of the digital watermark technology for embeddingwatermark information in audio content, a technique is employed, inwhich a pseudo random number sequence is generated by use of data calleda key, a frequency component in data of the audio contents is processedby use of this pseudo random number sequence to create a signal(watermark signal) containing desired watermark information, and thesignal is added to the data of the original audio content. Then, whendetecting the watermark information, a technique is employed, in whichthe frequency component of the data of the audio contents is processedby use of a pseudo random number sequence generated by the same key,detected values as a result of the processing are accumulated in thebuffer, then the watermark signal is extracted from the accumulatedvalues, and an embedded message (watermark information) is decoded.

The following documents are considered:

-   -   [Patent Document 1] Japanese Patent Laid-Open No. H11        (1999)-341452    -   [Patent Document 2] Japanese Patent Laid-Open No. 2002-320085

A length (time) of the accumulation of the detected values whendetecting the watermark information is usually one type of fixed length.For example, a detection apparatus is designed such that 30 seconds areset as a cycle of the accumulation and the detection result of thewatermark signal is outputted for every 30 seconds. Moreover, in adigital watermark technology for digital contents of a motion picture, atechnique of varying the length of the accumulation of detected valueswhen detecting watermark information is proposed (for example, refer toPatent Document 1). In this technology, watermark signals are weaklyembedded so as not to deteriorate equality of the motion picture, and atthe time of detection of the watermark information, the detected valuesare accumulated in a buffer until the detected values reach intensitysufficient for detecting the watermark information.

Moreover, in audio contents, there is one composed of a plurality ofchannels, such as one recorded in stereo. When the digital watermark isembedded in such audio contents, in general, one pseudo random numbersequence is generated by use of one key, audio data in the respectivechannels is processed by use of this one pseudo random number, and thusthe embedding is performed. Specifically, the same watermark signals areembedded in the audio data in the respective channels. In this case,when detecting the digital watermark, a technique is employed, in whichthe watermark signals are detected from the audio data in the respectivechannels and are synthesized, and an embedded message (watermarkinformation) is decoded. When the digital watermarks are embedded in therespective channels, detected values from the respective channels highlycorrelate with one another, and accordingly, a component of the messagein the detected values is intensified, thus facilitating the message tobe restored. Furthermore, in the case of using the digital watermarktechnology for the purpose of ensuring security, a technique isproposed, in which a plurality of digital watermarks are created by useof different keys depending on features of contents and a passage oftime thereof and are embedded in signals to be processed in order toenhance maintainability (for example, refer to Patent Document 2).

Meanwhile, audio contents converted into digital data are in themselvesdelivered through a broadcast and a network, or distributed by beingrecorded in a variety of recording media. In addition, audio contentsare provided by being processed in various ways such as used as a pieceof BGM (background music) of other contents and a jingle for a program.Hence, there are also audio contents which are extremely short in termsof time (for example, approximately two seconds), ones which aredeteriorated due to superposition of another sound thereon, and thelike.

Considering the existence of audio contents which are short in terms oftime, it is preferable that the embedding of a digital watermark inaudio contents also be performed for a short time span of the audiocontents. On the other hand, in order to detect a digital watermark fromaudio contents, which are subjected to the superposition of anothersound thereon and then deteriorated by being used as a piece of BGM andthe like, it is necessary that detected values from the audio contentsfor a somewhat long time (for example, approximately 30 seconds) beaccumulated (specifically, samples of the detected values be increased)and the watermark signal be intensified and then extracted.

However, when an accumulation cycle of the detected values is prolonged,the digital watermark embedded in the short audio contents cannot bedetected. For example, even when attempting to detect a digitalwatermark from audio contents of approximately two seconds in theaccumulation cycle set at 30 seconds, detected values, which come fromsounds other than the intended audio contents, are included in theaccumulated detected values for approximately 28 (=30−2)seconds.Accordingly, the message (watermark information) embedded in the audiocontents cannot be correctly detected.

The above-mentioned prior art, in which the accumulation cycle of thedetected values varies, has an aspect to intensify and combine theweakly embedded watermark signals by accumulating the signals until thesignals reach the intensity sufficient for detecting the watermarkinformation. In the prior art, to set an appropriate accumulation cyclefor detecting the watermark information individually from the shortaudio contents and the deteriorated audio contents is left out ofconsideration.

If audio contents are a stereo-recorded audio composition or the like,the same watermark signals are embedded in the audio data in therespective channels, as mentioned above. When the digital watermark isdetected, the watermark signals are detected from the audio data in therespective channels and synthesized, and then the message is restored.

However, when such audio contents are used as a piece of BGM of anarration, a sound of the narration superimposed on the audio contentshas a signal analogous to a monaural one in many cases, and thecorrelation between the audio data of the narration in the respectivechannels is high. Hence, when the detected values from the respectivechannels are synthesized together to intensify components of the highlycorrelated message, components of the narration sounds are alsointensified. Accordingly, it is difficult to distinguish between themessage components and the noise components (narration sounds) in thedetected values, there by making it difficult to restore the message.

In order to detect the watermark signals in such a case, it is necessaryto set a threshold value (a degree of correlation) for identifying thecomponents of the watermark signals among the detected values, to alarge one. However, when this threshold value is set to a large one, amuch higher correlation between the watermark signals in the respectivechannels will be required in order to detect the digital watermark, androbustness to the deterioration of the digital watermark will bereduced.

The above-mentioned prior art which creates the watermark signals by useof the different keys in response to the features of the contents andthe passage of time and embeds the created watermark signals in thesignals to be processed does not consider the deterioration when a soundanalogous to a monaural one, such as a narration, is superimposed on theaudio contents having a plurality of channels though the prior artembeds the different watermark signals in response to the features ofthe contents and the passage of time. Hence, when the digital watermarksare embedded in the audio data in the respective channels, the samewatermark signals using one key are likewise embedded in the audio datain the respective channels. Accordingly, the above-described problemcannot be solved.

SUMMARY OF THE INVENTION

To solve the above-described problems, it is an aspect of the presentinvention to improve robustness of a digital watermark embedded in audiocontents which are to be processed in various ways.

Moreover, it is another aspect of the present invention to provide amethod and a system for appropriately detecting the digital watermarkparticularly from audio contents short in terms of time or deterioratedaudio contents.

Furthermore, it is still another aspect of the present invention toprovide a method and a system for embedding and detecting a digitalwatermark particularly having a strong robustness to deterioration dueto superposition of another sound on audio contents.

In order to achieve the above-described aspects, the present inventionis realized as a digital watermark detection apparatus constituted asbelow. A digital watermark detection apparatus includes: a plurality ofwatermark signal detection units for individually calculating, for PCMdata in the respective channels of audio contents, detected values whichare correlation coefficients between frequency components of the PCMdata and pseudo random number sequences generated by a plurality of keysused to embed the digital watermark; a plurality of detected valueadding units for adding the detected values calculated by the pluralityof watermark signal detection units and corresponding to the respectivechannels and the respective keys for each possible combination of therespective channels and the respective keys; a comparison/selection unitfor receiving and comparing the respective results of the addition bythe plurality of detected value adding units with one another, andselecting and outputting one result of the addition; and a messagerestoration unit for restoring a message embedded as a digital watermarkbased on the result of the addition of the detected values, the resultbeing outputted from the comparison/selection unit, and detecting theaudio contents in which the digital watermark is embedded.

According to the present invention, the robustness of the digitalwatermarks embedded in audio contents processed in various ways can beimproved. Specifically, a method and system for appropriately detectinga digital watermark particularly from audio contents short in terms oftime or deteriorated audio contents can be provided. Moreover, a methodand system embedding and detecting a digital watermark particularlyhaving a strong robustness to deterioration due to superposition ofanother sound on audio contents.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantage thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view schematically showing an example of a hardwareconfiguration of a computer apparatus suitable for realizing apparatusin Embodiments 1 and 2;

FIG. 2 is a view showing a functional configuration of a digitalwatermark detection apparatus of Embodiment 1;

FIG. 3 is a flowchart showing a general detection procedure of watermarksignals from audio contents;

FIG. 4 is a view showing a state of integrating boundary detectionresults by a plurality of message restoration units in Embodiment 1;

FIG. 5 is a view for explaining relationships between results ofrestoring messages by the respective message restoration units and afinal detection result outputted from a detection result output unit inEmbodiment 1;

FIG. 6 is a view showing a functional configuration of a digitalwatermark embedding apparatus of Embodiment 2;

FIG. 7 is a flowchart showing a general embedding procedure of digitalwatermarks in audio contents;

FIG. 8 is a view showing a functional configuration of a digitalwatermark detection apparatus of Embodiment 2;

FIG. 9 is a view showing a configuration example of watermark signaldetection units and detected value adding units for detecting digitalwatermarks from monaural contents in Embodiment 2;

FIG. 10 is a view showing a functional configuration in a case ofselecting and outputting a best restoration result after restoring themessages in Embodiment 2;

FIG. 11 is a view showing a configuration example of a digital watermarkdetection apparatus formed by combining the respective configurations ofthe digital watermark detection apparatuses of Embodiments 1 and 2; and

FIG. 12 is a view showing a functional configuration in a case ofcombining the respective configurations of the digital watermarkdetection apparatuses of Embodiments 1 and 2 and selecting andoutputting the best restoration result after restoring the messages.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides systems, apparatus and methods to improverobustness of a digital watermark embedded in audio contents which areto be processed in various ways. Moreover, the present inventionprovides a method and a system for appropriately detecting the digitalwatermark particularly from audio contents short in terms of time ordeteriorated audio contents. Furthermore, the present invention providesa method and a system for embedding and detecting a digital watermarkparticularly having a strong robustness to deterioration due tosuperposition of another sound on audio contents.

In an example embodiment, the present invention is realized as a digitalwatermark detection apparatus. A digital watermark detection apparatusincludes: a plurality of watermark signal detection units forindividually calculating, for PCM data in the respective channels ofaudio contents, detected values which are correlation coefficientsbetween frequency components of the PCM data and pseudo random numbersequences generated by a plurality of keys used to embed the digitalwatermark; a plurality of detected value adding units for adding thedetected values calculated by the plurality of watermark signaldetection units and corresponding to the respective channels and therespective keys for each possible combination of the respective channelsand the respective keys; a comparison/selection unit for receiving andcomparing the respective results of the addition by the plurality ofdetected value adding units with one another, and selecting andoutputting one result of the addition; and a message restoration unitfor restoring a message embedded as a digital watermark based on theresult of the addition of the detected values, the result beingoutputted from the comparison/selection unit, and detecting the audiocontents in which the digital watermark is embedded.

Here, more preferably, in the plurality of detected value adding units,a detected value adding unit for outputting the detected valuecalculated by one of the watermark signal detection units as is, without adding the detected value to detected values calculated by the otherwatermark signal detection units, is included.

Moreover, from the results of the addition by the plurality of detectedvalue adding units, the comparison/selection unit selects the followingas the added results to be outputted.

One in which a sum of absolute values of the detected values is maximum.

One in which a sum of squares of the detected values is the maximum.

One in which the number of bits, an error has occurred therein, isminimum after performing error correction for the results of theaddition.

One in which a signal-to-noise ratio (SNR) is maximum found as a resultof performing error correction for the results of the addition andcalculating the SNRs by obtaining correct symbols of individual bits.

Furthermore, a configuration can be adopted, in which orders ofprocessing by the above-mentioned comparison/selection unit andprocessing by the message restoration unit are changed. In this case, aplurality of message restoration units are prepared, and the pluralityof message restoration units individually receive the results of theaddition by a plurality of detected value adding units, and restore themessages embedded as the digital watermarks. Then, thecomparison/selection unit receives and compares results of restoring themessages by the plurality of message restoration units, and selects andoutputs a series of messages.

Moreover, another embodiment of the present invention achieving theabove-described aspects is realized as a digital watermark detectionapparatus constituted as below. The digital watermark detectionapparatus includes: a watermark signal detection unit for calculating adetected value which is a correlation coefficient between a frequencycomponent of PCM data of audio contents and a pseudo random numbersequence generated by a key used to embed the digital watermark; aplurality of message restoration units for accumulating the detectedvalue calculated by the watermark signal detection unit in accumulationcycles different from one another, restoring the message embedded as thedigital watermark from the accumulated detected values, and moreover,performing boundary detections of the audio contents, and detecting theaudio contents in which the digital watermark is embedded; and adetection result output unit for receiving the respective processingresults by the plurality of message restoration units, and synthesizingand outputting detection results of the audio contents in the respectiveprocessing results, with the digital watermarks being embedded in theaudio contents.

Here, in more detail, when the audio contents in which the digitalwatermark is embedded are detected by any of the message restorationunits, the detection result output unit determines that the detectedaudio contents are the ones in which the digital watermark is embedded,and determines a portion where the audio contents in which the digitalwatermark is embedded are not detected by any of the message restorationunits as audio contents in which the digital watermark is not embedded.Moreover, when the audio contents in which the digital watermarks areembedded are detected by the plurality of message restoration units, adetection result by the message restoration unit of which accumulationcycle is shorter is prioritized. Furthermore, when the audio contents inwhich the digital watermark is embedded is detected by a predeterminedone of the message restoration units, a detection result by the messagerestoration unit is outputted without waiting for detections by theother message restoration units of which accumulation cycles are longerthan that of the message restoration unit.

Moreover, still another embodiment of the present invention achievingthe above-described aspects is realized as a digital watermark detectionmethod as below for detecting a digital watermark embedded in audiocontents by a computer. Specifically, the digital watermark detectionmethod includes: a first step of individually calculating, for PCM datain the respective channels of audio contents, detected values which arecorrelation coefficients between frequency components of the PCM dataand pseudo random number sequences generated by a plurality of keys usedto embed the digital watermark, and of storing the calculated detectedvalues in storing means; a second step of adding the calculated detectedvalues corresponding to the respective channels and the respective keysfor each possible combination of the respective channels and therespective keys, and of storing the added detected values in the storingmeans; a third step of receiving and comparing the respective results ofthe addition for each combination of the respective channels and therespective keys, and of selecting and outputting one result of theaddition; and a fourth step of restoring a message embedded as thedigital watermark based on the selected and outputted result of theaddition of the detected values, and moreover, of performing boundarydetection of the audio contents, and detecting the audio contents inwhich the digital watermark is embedded.

Furthermore, another digital watermark detection method according to thepresent invention includes: a first step of calculating a detected valuewhich is a correlation coefficient between a frequency component of PCMdata of audio contents and a pseudo random number sequence generated bya key used to embed the digital watermark, and of storing the detectedvalue in storing means; a second step of accumulating the calculateddetected value in accumulation cycles different from one another, ofrestoring a message embedded as the digital watermark from theaccumulated detected values, and moreover, of performing boundarydetection of the audio contents, of detecting the audio contents inwhich the digital watermark is embedded, and of storing detectionresults in the storing means; and a third step of receiving thedetection results based on the plurality of accumulation cycles, andsynthesizing and outputting detection results of the audio contents inthe respective processing results, with the digital watermarks beingembedded in the audio contents.

Moreover, the present invention is realized as a program for controllinga computer to execute processing corresponding to the respective stepsof the above-described digital watermark detection methods, or as aprogram for allowing the respective functions of the above-mentioneddigital watermark detection apparatuses to be realized by the computer.This program is provided by being stored in a magnetic disk, an opticaldisc, a semiconductor memory or other recording media and distributed,or by being distributed through a network.

According to the present invention constituted as described above, therobustness of the digital watermarks embedded in audio contentsprocessed in various ways can be improved. Specifically, a method andsystem for appropriately detecting a digital watermark particularly fromaudio contents short in terms of time or deteriorated audio contents canbe provided. Moreover, a method and system embedding and detecting adigital watermark particularly having a strong robustness todeterioration due to superposition of another sound on audio contents.

A best mode for carrying out the present invention (herein after, anembodiment) is described below in detail with reference to theaccompanying drawings.

Here, the following two embodiments are described in order to enhancerobustness of audio contents in consideration that the audio contentsare provided in various modes.

-   -   (Embodiment 1) Detection of digital watermark by use of        accumulation cycles    -   (Embodiment 2) Embedding and detection of digital watermark by        use of pseudo random number patterns        [Embodiment 1]

An embodiment in which a digital watermark is detected by use of aplurality of accumulation cycles is described.

when considering a mode of use of audio contents, audio contentsdeteriorated due to superposition of another sound thereon, such asaudio contents used as a BGM, are audio contents having some length interms of time. Mean while, audio contents of approximately two seconds,which are extremely short in terms of time, are used as a jingle or asound effect for a broadcast program and hardly superposed on anothersound. In other words, it can be said that, while it is necessary toaccumulate detected values in a long accumulation cycle in order to copewith deterioration of audio contents having some length in terms of timeand thus to restore a message (watermark information), the message canbe restored relatively satisfactorily even from detected valuesaccumulated in a short accumulation cycle, in the audio contents shortin terms of time.

Moreover, as described in the “Problems to be Solved by the Invention,”when the accumulation cycle of the detected values is prolonged, itbecomes difficult to restore the message from audio contents short interms of time.

Accordingly, in this embodiment, detected values of watermark signalsare accumulated in a plurality of different accumulation cycles. Audiocontents which are short interms of time and resistant to deteriorationand audio contents which have some length in terms of time and have apossibility of deterioration are coped with by means of appropriateaccumulation cycles, and the message is restored.

FIG. 1 is a view schematically showing an example of a hardwareconfiguration of a computer apparatus suitable for realizing the digitalwatermark detection apparatus according to this embodiment.

The computer apparatus shown in FIG. 1 includes a central processingunit (CPU) 101 as arithmetic means, a main memory 103, a video card 104,a magnetic disk device (HDD) 105, a network interface 106, a flexibledisk drive 108, and a keyboard/mouse 109. The main memory 103 isconnected to the CPU 101 through a mother board (M/B) chip set 102 and aCPU bus. The video card 104 is connected to the CPU 101 through the sameM/B chip set 102 and an accelerated graphics port (AGP). Moreover, theHDD 105 and the network interface 106 are connected to the M/B chip set102 through a peripheral component interconnect (PCI) bus. Furthermore,the flexible disk drive 108 and the keyboard/mouse 109 are connected tothe M/B chip set 102 through the PCI bus, a bridge circuit 107, and alow-speed bus such as an industry standard architecture (ISA) bus.

Note that FIG. 1 only illustrates the hardware configuration of thecomputer apparatus which realizes this embodiment, and other variousconfigurations can be adopted as long as this embodiment is applicablethereto. For example, a configuration may be made, in which only a videomemory is mounted instead of providing the video card 104, and imagedata is processed in the CPU 101. Alternatively, as an external storagedevice, a drive for a compact disc recordable (CD-R) or a digitalversatile disc random access memory (DVD-RAM) may be provided through aninterface such as AT attachment (ATA) or small computer system interface(SCSI).

FIG. 2 is a view showing a functional configuration of the digitalwatermark detection apparatus of this embodiment.

Referring to FIG. 2, the digital watermark detection apparatus 10 ofthis embodiment includes: watermark signal detection units 11 providedfor each of channels, which detect watermark signals from data of therespective channels of the audio contents; a detected value adding unit12 which adds detected values of the watermark signals detected by therespective watermark signal detection units 11; a plurality of messagerestoration units 13 which accumulate the obtained watermark signals andrestore messages from the accumulated watermark signals; and a detectionresult output unit 14 which performs comparison processing forrestoration results by the respective message restoration units 13 andoutputs a comparison result as a final detection result.

The watermark signal detection units 11 are realized, for example, bythe CPU 101 which is shown in FIG. 1 and controlled by a program, anddetect watermark signals embedded in the data of audio contents. For adetection method of watermark signals, a detection method in an existingdigital watermark technology can be used.

FIG. 3 is a flowchart showing a general detection procedure of watermarksignals for audio contents.

As shown in FIG. 3, each of the watermark signal detection units 11first receives pulse code modulation (PCM) data of the audio contents(Step 301), and performs a Fourier transform on the received data toextract frequency components thereof (Step 302). Then, the watermarksignal detection unit 11 normalizes data of the obtained frequencycomponents, and acquires a mean amplitude for each portion of the audiodata (Step 303). Next, the watermark signal detection unit 11 calculatesa correlation between a pseudo random number sequence generated by arandom number generator by use of the same key as the one used when thedigital watermark is embedded and the mean amplitude of the frequencycomponents, which is obtained in Step 303 (Step 304), and outputs acalculation result (correlation coefficient) as a detected value of thewatermark signal (Step 305).

The calculated detected value is temporarily stored in a storage device,for example, such as the main memory 103 and a cache memory of the CPU101 in FIG. 1.

The detected value adding unit 12 is realized, for example, by the CPU101 which is shown in FIG. 1 and controlled by a program, and receivesand adds together the detected values of the watermark signals detectedby the respective watermark signal detection units 11 provided for eachof the channels. The added detected value is temporarily stored in astorage device, for example, such as the main memory 103 and the cachememory of the CPU 101 in FIG. 1. Note that, in the example shown in FIG.2, the audio contents are assumed to be one recorded in stereo, and thetwo watermark signal detection units 11 for a left and right audio aredescribed. However, needless to say, the number of watermark signaldetection units 11 is not limited to that in the illustrated example.The watermark signal detection units 11 can be provided in numbercorresponding to the number of channels of audio contents, and in thecase of monaural audio contents, one watermark signal detection unit 11may be provided. When one watermark signal detection unit 11 isprovided, the adding processing of detected values is unnecessary, andthe detected value adding unit 12 is not an essential constituentelement.

Each of the message restoration units 13 is realized, for example, bythe CPU 101 and the storing means such as the main memory 103 which areshown in FIG. 1, accumulates the detected value of the watermark signaladded by the detected value adding unit 12 (the detected value extractedby the watermark signal detection unit 11 when only a watermark signaldetection unit 11 is provided) in a buffer realized by the main memory103 or the like till an amount for a certain period of time, andrestores the message based on the detected values accumulated andintensified together. Specifically, when the received detected value(correlation coefficient between the mean amplitudes of the frequencycomponents of the PCM data and the pseudo random number sequencegenerated by use of the key) is larger than a preset threshold value, itis determined that the watermark is embedded, and the message isrestored from such a detected value. For a restoring method of themessage, a restoring method in an existing digital watermark technologycan be used.

Moreover, the message restoration units 13 detect boundaries of theaudio contents based on the respective restoration results of themessages. The restoring of the messages and the detection of theboundaries of the audio contents are performed, and thus the audiocontents in which the digital watermarks are embedded are detected.Portions which are not determined to be audio contents in which thedigital watermarks are embedded in the PCM data are determined to beaudio contents in which the digital watermarks are not embedded.

In this embodiment, as shown in FIG. 2, the plurality of messagerestoration units 13 are provided, and the accumulation cycles for thedetected values are made to differ from one another. In the illustratedexample, three types of message restoration units 13 which individuallyhave a reference accumulation cycle, an accumulation cycle twice as muchas the reference and an accumulation cycle four times as much as thereference are described. However, needless to say, the number of messagerestoration units 13 and the accumulation cycles are not limited tothose in the illustrated example. Note that, in the description below,when it is necessary to distinguish the respective message restorationunits 13 from one another, a suffix is added to the respective messagerestoration units 13. The message restoration unit 13 which has thereference accumulation cycle is written as a message restoration unit 13a, the message restoration unit 13 which has the accumulation cycletwice as much as the reference is written as a message restoration unit13 b, and the message restoration unit 13 which has accumulation cyclefour times as much as the reference is written as a message restorationunit 13 c. Mean while, in the case where it is unnecessary todistinguish these message restoration units, these message restorationunits are simply written as the message restoration units 13.

As described above, audio contents deteriorated due to superposition ofanother sound thereon have some length in terms of time, andaccordingly, the message restoration units 13 of which accumulationcycles are long are provided in order to cope with such audio contentshaving a possibility of deterioration. Therefore, as accumulation cyclesof message restoration units 13 become higher, threshold values forrestoring the messages from detected values may be set higher. Thus, themessage restoration unit 13 b becomes less prone to be affected by aninfluence of the deterioration caused by superposition of another soundthereon than the message restoration unit 13 a, the message restorationunit 13 c becomes less prone than the message restoration unit 13 b, andnoise due to the deterioration is removed appropriately, thus making itpossible to restore the messages correctly.

The messages restored by the respective message restoration units 13 areindividually held temporarily in storage device such as, for example,the main memory 103 and the cache memory of the CPU 101 in FIG. 1.

The detection result output unit 14 is realized, for example, by the CPU101 which is shown in FIG. 1 and controlled by a program. The detectionresult output unit 14 compares and integrates the detection results ofthe audio contents in which the digital watermarks are embedded, theresults being obtained by the plurality of message restoration units 13,and creates and outputs the final detection result according to thefollowing rules.

Rule 1: When the audio contents in which the digital watermark isembedded are detected by any of the message restoration units 13, thedetection result output unit 14 determines the audio contents as audiocontents in which the digital watermark is embedded, and outputs thedetection result. Specifically, only when the audio contents in whichthe digital watermark is embedded are not detected by any of the messagerestoration units 13, the detection result output unit 14 determines theportion concerned as the audio contents in which the digital watermarkis not embedded.

Rule 2: When the audio contents in which the digital watermark isembedded are detected by the plurality of message restoration units 13,the detection result output unit 14 prioritizes the detection result bya message restoration unit 13 of which accumulation cycle is shorter.Specifically, when contents of the messages restored by a plurality ofmessage restoration units 13 contradict one another, the detectionresult output unit 14 employs the message restored by a messagerestoration unit 13 of which accumulation cycle is shorter as thedetection result.

Rule 3: When the audio contents in which the digital watermark isembedded is detected by a predetermined message restoration unit 13, thedetection result output unit 14 outputs the detection result withoutwaiting for detection of the audio contents in which the digitalwatermark is embedded by the other message restoration unit 13 of whichaccumulation cycle is longer than that of the predetermined messagerestoration unit 13. This is because the detection result by a messagerestoration unit 13 of which accumulation cycle is shorter isprioritized by Rule 2, and thus the detection result by a messagerestoration unit 13 of which accumulation cycle is longer does notaffect the final detection result by the detection result output unit14.

Moreover, in the integration processing of the detection results, thedetection result output unit 14 integrates results of the boundarydetection of the audio contents by the respective message restorationunits 13, and performs appropriate boundary detection.

FIG. 4 is a view showing a state of integrating boundary detectionresults by the message restoration units 13 a and 13 b. Note that themessage restoration units 13 a and 13 b determine the existence of thewatermark information and restore the watermark information based on thedetected values accumulated in each of the accumulation cycles.Moreover, as shown in FIG. 4, it is assumed that the message restorationunits 13 a and 13 b accumulate the detected values for the amountcorresponding to the respective accumulation cycles by use of aplurality of buffers while slightly shifting the time. Thus, highlyprecise boundary detection can be performed by using shifts inaccumulating time between the respective buffers as a unit without usingthe accumulation cycles of the respective message restoration units 13as a unit.

The following case is assumed: where there is PCM data in which audiocontents [1] having no digital watermark embedded therein, audiocontents [2] having a message A embedded therein, and audio contents [3]having a message B embedded therein continue in such an order of [1],[3], [1], [3] and [2].

In this case, referring to FIG. 4, it is understood that the messagerestoration unit 13 a was not able to detect audio contents [3] whichappeared first between audio contents [3] which appeared twice. Thismeans that the message B in the audio contents [3] was not able to berestored from detected values accumulated in the short accumulationcycle because the audio contents [3] had some length and weredeteriorated.

However, the message B in the audio contents [3] concerned is detectedby the message restoration unit 13 b having a longer accumulation cycle.Hence, according to the above-described Rule 1, the boundary of theaudio contents is determined based on the detection result by themessage restoration unit 13 b.

Mean while, it is understood that the message restoration unit 13 b wasnot able to detect the audio contents [2] which appeared finally in thePCM data. This means the following: the audio contents [3] whichappeared immediately before the audio contents [2] concerned arecontained in the accumulation cycle because the audio contents [2] areextremely short; the message A in the audio contents [2] and the messageB in the audio contents [3] are mixed in the detected value; and thusthe message A was not able to be restored. Note that, as a generalaction of the message restoration units 13, a current state ismaintained until a message different from a current message is restoredor until it is settled that a different message is not restored, andaccordingly, in the detection result by the message restoration unit 13b in FIG. 4, the audio contents [3] are maintained.

However, the message A in the audio contents [2] concerned is detectedby the message storing unit 13 a having the short accumulation cycle.Therefore, according to the above-mentioned Rule 2, the boundary of theaudio contents is determined based on the detection result by themessage restoration unit 13 a.

An action of the detection result output unit 14 is described below indetail by giving a specific detection example.

FIG. 5 is a view for explaining relationships between results ofrestoring the messages by the respective message restoration units 13and a final detection result outputted from the detection result outputunit 14.

In FIG. 5, in the PCM data to be processed, as in the case of FIG. 4,audio contents [1] in which no digital watermark is embedded, audiocontents [2] in which a message A is embedded, and audio contents [3] inwhich a message B is embedded, are contained. Moreover, the PCM data inthe illustrated range is separated into eight sections from Sections Ito VIII based on results of detecting boundaries. The respectiveSections are examined.

In Section I, no message is restored in any of the respective messagerestoration units 13 a, 13 b and 13 c. Accordingly, a final detectionresult of Section I also becomes the audio contents [1] in which nomessage is embedded.

In Section II, the message A is restored by the message restoration unit13 a, and accordingly, a final detection result of Section II becomesthe audio contents [2] in which the message A is embedded according tothe above-mentioned Rules 2 and 3. Moreover, a length of Section II isdetermined based on the boundary detection result by the messagerestoration unit 13 a.

In Section III, no message is restored in any of the respective messagerestoration units 13 a, 13 b and 13 c. Accordingly, a final detectionresult of Section III also becomes the audio contents [1] in which nomessage is embedded.

In Section IV, the messages B are restored by the message restorationunits 13 b and 13 c, and accordingly, a final detection result ofSection IV becomes the audio contents [3] in which the message B isembedded according to the above-mentioned Rule 1. Moreover, a length ofSection IV is determined in a manner that a section of the audiocontents [3] (section where the message 6B is restored) by a boundarydetection result of the message restoration unit 13 c and a section ofthe audio contents [3] by a boundary detection result of the messagerestoration unit 13 b are superposed on each other.

In Section V, no message is restored in any of the respective messagerestoration units 13 a, 13 b and 13 c. Accordingly, a final detectionresult of Section V also becomes the audio contents [1] in which nomessage is embedded.

In Section VI, the messages B are restored by the message restorationunits 13 a and 13 b, and accordingly, a final detection result ofSection VI becomes the audio contents [3] in which the message B isembedded according to the above-mentioned Rule 1. A length of Section VIis explained in combination with that of the next Section VII.

In Section VII, the message A is restored by the message restorationunit 13 a. Moreover, in apart of Section VII, the message B is restoredby the message restoration unit 13 b. Detection results by the messagerestoration unit 13 a and the message restoration unit 13 b contradicteach other. However, the detection result by the message restorationunit 13 a of which accumulation cycle is shorter is prioritizedaccording to the above-mentioned Rule 2, and a final detection result ofSection VII becomes the audio contents [2] in which the message A isembedded.

Here, the lengths of Sections VI and VII are described. When assuming asection formed by adding Sections VI and VII, the message restorationunit 13 b restores the message B from Section VI to a part of SectionVII, and performs the boundary detection while regarding this describedsection as a section of the audio contents [3]. Mean while, the messagerestoration unit 13 a restores the message B and the message A, andperforms the boundary detection while regarding the section where themessage B is restored as a section of the audio contents [3] and thesection where the message A is restored as a section of the audiocontents [2]. Rules 2 and 3 are applied to these boundary detectionresults, and the lengths of Sections VI and VII are determined based onthe boundary detection results by the message restoration unit 13 a.

In Section VIII, no message is restored in any of the respective messagerestoration units 13 a, 13 b and 13 c. Accordingly, a final detectionresult of Section VIII also becomes the audio contents [1] in which nomessage is embedded.

As described above, in this embodiment, messages embedded in audiocontents by digital watermarks are restored by use of the plurality ofmessage restoration units 13 having different accumulation cycles. Thus,a message restoration unit 13 of which accumulation cycle is shortercopes with audio contents short in terms of time, and a messagerestoration unit 13 of which accumulation cycle is longer copes withaudio contents which have some length and a possibility ofdeterioration, thus making it possible to restore the messages embeddedin the audio contents.

Moreover, because the audio contents short in terms of time have lesspossibility of deterioration due to superposition of another soundthereon, this embodiment prioritizes the detection result by the messagerestoration unit 13 of which accumulation cycle is shorter, which copeswith the audio contents short in terms of time. Then, when the messageis restored and the digital watermark is detected by the messagerestoration unit 13 of which accumulation cycle is shorter, thedetection result is outputted without waiting for the restoring of themessage by the other message restoration units 13. Therefore, a timerequired for detecting the digital watermark can be shortened by notwaiting for the restoring of the message by the message restorationunits 13 of which accumulation cycles are longer. [Embodiment 2]

Next, an embodiment of embedding and detecting a digital watermark byuse of a plurality of pseudo random number patterns is described.

A digital watermark embedding apparatus and a digital watermarkdetection apparatus according to this embodiment, are realized, forexample, by the computer apparatus as in FIG. 1, which is shown inEmbodiment 1.

FIG. 6 is a view showing a functional configuration of the digitalwatermark embedding apparatus of this embodiment.

Referring to FIG. 6, a digital watermark embedding apparatus 20 of thisembodiment includes a watermark signal creating unit 21 which createsthe watermark signal to be embedded in audio contents, and an addingunit 22 which adds the created watermark signal and original audiocontents together to create audio contents in which the digitalwatermark is already embedded. In this embodiment, a plurality ofdigital watermarks are embedded in audio data in the plurality ofrespective channels in the audio contents composed of the channelsconcerned. A configuration shown in FIG. 6 is a configuration forembedding digital watermarks in audio data of one channel. Moreover, foran embedding method of digital watermarks in the respective channels, anembedding method in an existing digital watermark technology can beused.

FIG. 7 is a flowchart showing a general embedding procedure of watermarksignals in audio contents. As shown in FIG. 7, a watermark signalcreating unit 21 first receives PCM data as an aspect to be processed(Step 701), and performs a Fourier transform on the received data toextract frequency components thereof, thus obtaining an auditory model(Step 702). Then, by use of this auditory model, the watermark signalcreating unit 21 obtains an imperceptible non-audible changing amount(Step 703). Next, the watermark signal creating unit 21 changesfrequency components of the PCM data extracted in Step 702, based on thenon-audible changing amount obtained in Step 703 and a pseudo randomnumber sequence generated by a random number generator by use of apredetermined key, thus creating watermark signals in the frequencydomain (Step 704). Then, the watermark signal creating unit 21 performsan inverse Fourier transform on the obtained watermark signals in thefrequency domain, thus creating watermark signals in the time domain(Step 705).

When the watermark signals are created, the adding unit 22 adds togetherthe PCM data as the aspect to be processed and the watermark signals inthe time domain, which are created by the watermark signal creating unit21, thus creating PCM data in which the digital watermarks are alreadyembedded (Step 706).

Here, in this embodiment, the digital watermarks are embedded in the PCMdata of the respective channels according to the above-describedprocedure, and in Step 704, the watermark signal creating unit 21creates the pseudo random number sequence for the respective channels byuse of a plurality of keys, thus creating the watermark signals. Hence,the digital watermarks embedded in the respective channels differ in thewatermark signals added to the original PCM data though messages thereofare the same. Note that, in order to allow the watermark signals addedto the data of the respective channels to entirely differ from oneanother, the number of keys is equalized to the number of channels ofthe audio contents.

FIG. 8 is a view showing a functional configuration of the digitalwatermark detection apparatus of this embodiment. Referring to FIG. 8,the digital watermark detection apparatus 30 of this embodimentincludes: watermark signal detection units 31 which detect the watermarksignals from the data of the respective channels of the audio contents;detected value adding units 32 which add together detected values of thewatermark signals detected by the watermark signal detection units 31; acomparison/selection unit 33; and a plurality of message restorationunits 34 which accumulate the obtained watermark signals and restoremessages from the accumulated watermark signals.

In this embodiment, as described above, the digital watermarks areembedded in the plurality of channels of the audio contents by thewatermark signals created by use of the plurality of keys. Accordingly,the digital watermark detection apparatus 30 of this embodiment detectsthe watermark signals from the data of the respective channels of theaudio contents by use of the respective keys used for embedding thedigital watermarks. Then, the digital watermark detection apparatus 30synthesizes the obtained detected values in various ways of possiblecombinations, selects appropriate combinations, and restores themessages. Hereinafter, for simplicity, it is assumed that the audiocontents are recorded in two-channel stereo (channels L and R), anddescription is made by taking as an example the case where digitalwatermarks are embedded in the data of the respective channels by use ofwatermark signals created by two keys (K1 and K2).

The watermark signal detection units 31 are realized, for example, bythe CPU 101 which is shown in FIG. 1 and controlled by a program, anddetect watermark signals embedded in the data of the audio contents. Fora detection method of watermark signals, a detection method in anexisting digital watermark technology, for example, the detection methodaccording to the procedure shown in FIG. 3, which is described inEmbodiment 1, can be used. Obtained detected values are temporarily heldin a storage device such as, for example, the main memory 103 and thecache memory of the CPU 101 in FIG. 1.

Here, in this embodiment, it is necessary to detect the watermarksignals created in the data of the two channels (L and R) by use of thekeys (K1 and K2) different from each other. It is not known, in the dataof each of the two channels, which of the keys is used for the embeddingof watermarks. Accordingly, for the data of each channel, a watermarksignal detection unit 31 which detects watermark signals by use of thekey K1 and a watermark signal detection unit 31 which detects watermarksignals by use of the key K2 are individually prepared. In FIG. 8, fourwatermark signal detection units 31 are illustrated because twowatermark signal detection units 31 are provided for each channel.Herein after, in the case of distinguishing these watermark signaldetection units 31 from one another, types of the channels and the keysare added thereto as suffix, and the watermark signal detection unitsare denoted such as watermark signal detection unit 31LK1 and watermarksignal detection unit 31RK2. Mean while, in the case where it isunnecessary to distinguish these watermark signal detection units, thesewatermark signal detection units are simply denoted as watermark signaldetection units 31.

Note that, though the four watermark signal detection units 31 areillustrated in FIG. 8 as described above, in general, the number of keysis n when the number of channels is n, and accordingly, it is necessaryto prepare n² pieces of watermark signal detection units 31.

Moreover, a configuration is also conceivable, in which informationindicating which of the keys is used for the embedding of digitalwatermarks is provided in the data of the respective channels from thedigital watermark embedding apparatus 20 to the digital watermarkdetection apparatus 30, and thus the number of watermark signaldetection units 31 are reduced. However, when considering that the dataof the respective channels change places with each other by onlychanging cables on instruments on a path where the audio contents aredistributed, it is preferable to prepare the four watermark signaldetection units 31 described above.

The detected value adding units 32 are realized, for example, by the CPU101 which is shown in FIG. 1 and controlled by a program, and add thedetected values of watermark signals obtained by the above-mentionedplurality of watermark signal detection units 31 in all possiblecombinations. The calculated detected values are temporarily held in astorage device such as, for example, the main memory 103 and a cachememory of the CPU 101 in FIG. 1.

Here, when the watermarks are embedded in the data of the two channels(L and R) by use of the keys (K1 and K2) different from each other, itis understood that the different keys are used for the data of therespective channels, and accordingly, possible combinations are two,which are: a combination of the detected values by the watermark signaldetection units 31LK1 and 31RK2; and a combination of the detectedvalues by the watermark signal detection units 31LK2 and 31RK1. Hence,as shown in FIG. 8, two detected value adding units 32 which adddetected values in these two combinations are prepared.

In general, a combination of the same channels or the same keys has nopossibility to be present, and accordingly, the number of possiblecombinations is n!, and it is necessary to prepare n! pieces of detectedvalue adding units 32.

Incidentally, when the audio contents from which digital watermarks areto be detected are received as one-channel monaural contents though theaudio contents are originally two-channel stereo contents, possiblecombinations differ from those in the above-described case.

FIG. 9 is a view showing a configuration example of watermark signaldetection units 31 and detected value adding units 32 for detectingdigital watermarks from monaural contents.

In the monaural contents, digital watermarks are embedded by thewatermark signals created by use of the key K1 or the key K2 as in theabove-described case, and accordingly, two watermark signal detectionunits 31 are used, which are: a watermark signal detection unit 31MK1which detects watermark signals from the one-channel (channel M) data byuse of the key K1; and a watermark signal detection unit 31MK2 whichdetects watermark signals therefrom by use of the key K2.

As a mode in which the two-channel stereo contents are converted intothe one-channel monaural content, there are two cases, which are: a casewhere the data of the two channels are added together; and a case whereany one of the data of the two channels is deleted. Therefore, as casesof monaural contents, there are cases which are: a case where both ofthe digital watermarks using the key K1 and the key K2 are embedded; acase where digital watermarks using the key K1 is embedded; and a casewhere digital watermarks using the key K2 is embedded. Accordingly, adetected value adding unit 32 which adds together the detected values bythe watermark signal detection units 31MK1 and 31MK2 in combination witheach other, a detected value adding unit 32 which receives the detectedvalue by the watermark signal detection unit 31MK1 and outputs thedetected value as is, and a detected value adding unit 32 which receivesthe detected value by the watermark signal detection unit 31MK2 andoutputs the detected value as is, are prepared. Note that watermarksignal detection units 32 which output one of the detected values by thewatermark signal detection unit 31MK1 and the detected value by thewatermark signal detection unit 31MK2 as is are not essentialconstituent elements, and it is also possible to allow a storage deviceto hold the detected values by one of the watermark signal detectionunit 31MK1 and the watermark signal detection unit 31MK2 as is and toallow the comparison/selection unit 33 to be described later to processthe detected values.

The comparison/selection unit 33 is realized, for example, by the CPU101 which is shown in FIG. 1 and controlled by a program, compares theoutputs of the respective detected value adding units 32 with oneanother, and selects and outputs best detected values. The selected bestdetected values are temporarily held in a storage device such as, forexample, the main memory 103 and a cache memory of the CPU 101 in FIG.1.

Although various methods are conceivable as a technique of selecting thebest detected values, for example, the following methods can be adopted.

-   -   Defining a value in which the sum of absolute values of the        detected values is maximum as the best detected value.    -   Defining a value in which the sum of squares of the detected        values is maximum as the best detected value.    -   Performing error correction for the detected values, and        defining a value in which the number of bits, an error has        occurred therein, is minimum as the best detected value.    -   Performing the error correction for the detected values,        calculating signal-to-noise ratios (SNRs) by obtaining correct        symbols of individual bits, and defining a value in which the        obtained SNR is maximum as the best detected value.

The message restoration unit 34 is realized, for example, by the CPU 101which is shown in FIG. 1 and controlled by a program, accumulates thebest detected values selected in the comparison/selection unit 33 in abuffer realized by the main memory 103 or the like till an amount for acertain period of time, and restores massages based on the detectedvalues accumulated and intensified together. Specifically, when thereceived values (or correlation coefficients between a mean amplitude offrequency components of a PCM data and a pseudo random number sequencegenerated by use of a key) are larger than a preset threshold value, themessage restoration unit 34 determines that digital watermarks areembedded, and restores the messages from such detected values. For arestoring method of messages, a restoring method in an existing digitalwatermark technology can be used. Moreover, the message restoration unit34 performs boundary detection of audio contents based on restorationresults of the respective messages. Then, the restored messages andboundary detection results are outputted as a final detection result.

In such a way, the embedding of digital watermarks using a plurality ofpseudo random number patterns and the detection of such digitalwatermarks are realized. As described above, digital watermarks embeddedby use of pseudo random number patterns by use of a plurality of keysare detected from data processed by the pseudo random number patterns bythe keys for use when the digital watermarks are embedded. Specifically,in order to detect watermark signals from the data of the plurality ofchannels, different pieces of processing by different keys areimplemented for the data of the respective channels in the watermarksignal detection units 31. Therefore, even if a sound analogous to amonaural sound, such as a narration, is superposed on audio contents,the superposed sound becomes data sequences completely different fromeach other for each of the channels through the processing by pseudorandom number patterns generated by use of the keys, and the correlationthere between becomes lowered. Hence, while components of watermarksignals in the detected values are intensified together by being addedtogether in detected value adding units 32, components of audio datasuperposed on the audio contents are not intensified together, andaccordingly, it becomes easy to detect watermark signals.

In this embodiment, digital watermarks are embedded in respective piecesof data of a plurality of channels of audio contents by watermarksignals created by use of keys different from each other. However, whenaudio contents are two-channel stereo contents, a configuration may beadopted, in which a pseudo random number sequence generated by use of akey is allowed to change sign and to be used as two pseudo random numbersequences, and watermark signals are created and embedded in the data ofthe respective channels. In such a way, when detecting the digitalwatermarks, differences between the detected values by the watermarksignal detection units 31 in the respective channels are subtracted, andthus influences of the monaural sounds superposed on the audio contentsare cancelled each other out. Only the components of the watermarksignals in the detected values can be intensified together, and itbecomes easier to detect the watermark signals.

Moreover, when embedding watermark signals in the data of the respectivechannels, it is also possible to perform a so-called permutationencryption. In this case, permutation is performed and decryption of thewatermark information is performed when the detected values by thewatermark signal detection units 31 are added together in detected valueadding units 32. In such a way, security of digital watermarks can beenhanced.

Moreover, when completely different audio contents are individuallyrecorded in a plurality of channels, there is also a possibility thatthe components of the watermark signals in the detected values are notappropriately intensified together even if the detected values from thedata of the respective channels are added together. Accordingly, in ause environment where there is a possibility of receiving such audiocontents as aspects from which digital watermarks are to be detected, itis preferable to set not only the values obtained by adding together thedetected values from the data of the respective channels but also thedetected values from the data of the respective channels as they are asaspects to be processed in the comparison/selection unit 33.

In the functional configuration of the digital watermark detectionapparatus 30 according to this embodiment, which is shown in FIG. 8, thecomparison/selection unit 33 compares the respective adding results ofthe detected values added together for each of the possible combinationsof the respective channels and keys in the detected value adding units32, and selects an adding result, and the message restoration unit 34restores the messages of the digital watermarks from the selected addingresult. However, a configuration can be adopted, in which the bestrestoration result is selected and outputted after restoring themessages.

FIG. 10 is a view showing a functional configuration when the bestrestoration result is selected and outputted after restoring themessages. In FIG. 10, watermark signal detection units 31 and detectedvalue adding units 32 are similar to the watermark signal detectionunits 31 and the detected value adding units 32, which are describedwith reference to FIG. 8, and accordingly, the same reference numeralsare added thereto, and description thereof is omitted.

A plurality of message restoration units 41 are realized, for example,by the CPU 101 which is shown in FIG. 1 and controlled by a program, andare provided so as to correspond to the detected value adding units 32.Then, the message restoration units 41 individually receive addingresults by the plurality of detected value adding units 32, accumulatethe adding results till an amount for a certain period of time in abuffer realized by the main memory 103 and the like, and restore themessages based on the detected values accumulated and intensifiedtogether. For a restoring method of the messages, a restoring method inan existing digital watermark technology can be used as in the messagerestoration unit 34 shown in FIG. 8. Moreover, the message restorationunits 41 perform the boundary detection of audio contents based on therespective restoration results of the messages. The restored messagesare temporarily held in a storage device such as, for example, the mainmemory 103 and a cache memory of the CPU 101 in FIG. 1.

A comparison/selection unit 42 is realized, for example, by the CPU 101which is shown in FIG. 1 and controlled by a program, compares therestoration results of the messages by the plurality of messagerestoration units 41, and selects and outputs appropriate series ofmessages. For a selection method of the messages, various methods areconceivable. For example, a message embedded by the digital watermarkembedding apparatus 20 is given to the digital watermark detectionapparatus 30 in advance, and this message and the messages restored bythe respective message restoration units 41 are individually compared,and thus a coinciding one can be selected. Moreover, whether or not themessages are meaningful can be determined based on an intended purposeof the digital watermarks (for example, displaying an origin of thecontents), and thus a meaningful message can be selected.

As above, Embodiment 1 which performs the detection of the digitalwatermark by use of the plurality of accumulation cycles and Embodiment2 which performs the embedding and detection of the digital watermark byuse of the plurality of pseudo random number patterns are described. Itis also possible to constitute a digital watermark detection apparatusby combining these embodiments.

FIG. 11 is a view showing a configuration example of a digital watermarkdetection apparatus formed by combining the configuration of the digitalwatermark detection apparatus 10 of Embodiment 1 and the configurationof the digital watermark detection apparatus 30 shown in FIG. 8 inEmbodiment 2. As shown in FIG. 11, this digital watermark detectionapparatus includes: watermark signal detection units 31 which detect thewatermark signals by use of the pseudo random number sequence generatedfrom the data of the respective channels of the audio contents by aplurality of keys; detected value adding units 32 which add together thedetected values of the watermark signals detected by the watermarksignal detection units 31; and a comparison/selection unit 33. Moreover,the digital watermark detection apparatus includes: a plurality ofmessage restoration units 13 which accumulate the best detected valuesselected by the comparison/selection unit 33 in a plurality ofaccumulation cycles and restore the messages from the accumulatedwatermark signals; and a detection result output unit 14 which performscomparison processing for restoration results by the respective messagerestoration unit 13 and outputs the comparison result as a finaldetection result.

Note that the watermark signal detection units 31, the detected valueadding units 32 and the comparison/selection unit 33 are similar to thewatermark signal detection units 31, the detected value adding units 32and the comparison/selection unit 33, which are described in Embodiment2, and the message restoration units 13 and the detection result outputunit 14 are similar to the message restoration units 13 and thedetection result output unit 14, which are described in Embodiment 1.Hence, the same reference numerals are added to these components, anddetailed description thereof is omitted.

In the digital watermark detection apparatus of FIG. 11 also, as in theconfiguration example shown in FIG. 10, a configuration can be adopted,in which the best restoration result is selected and outputted afterrestoring the messages.

FIG. 12 is a view showing a functional configuration in the case ofcombining the configuration of the digital watermark detection apparatus10 of Embodiment 1 and the configuration of the digital watermarkdetection apparatus 30 shown in FIG. 8 in Embodiment 2 and selecting andoutputting the best restoration result after restoring the messages. InFIG. 12, watermark signal detection units 31 and detected value addingunits 32 are similar to the watermark signal detection units 31 and thedetected value adding units 32, which are described in Embodiment 2, anda detection result output unit 14 is similar to the detection resultoutput unit 14 described in Embodiment 1. Hence, the same referencenumerals are individually added to these components, and detaileddescription thereof is omitted.

The message restoration units 51 are realized, for example, by the CPU101 which is shown in FIG. 1 and controlled by a program, and theplurality thereof are provided so as to correspond to the detected valueadding units 32 and in a similar way to the message restoration units 13shown in FIG. 2 in Embodiment 1. Specifically, in the example of FIG.12, three types of message restoration units 51 which have a referenceaccumulation cycle, an accumulation cycle twice as much as the referenceand an accumulation cycle four times as much as the reference areprovided for each of the outputs of the respective detected value addingunits 32. In total, six message restoration units 51 are provided.

Comparison/selection units 52 are realized, for example, by the CPU 101which is shown in FIG. 1 and controlled by a program, and the pluralitythereof are provided so as to correspond to the accumulation cycles ofthe message restoration units 51, which are different from one another.Then, for each of the accumulation cycles, the comparison/selectionunits 52 receive and compare the restoration results of the messages bythe plurality of message restoration units 51, and select and outputseries of appropriate messages. The outputs of the respectivecomparison/selection units 52 are individually inputted to the detectionresult output unit 14 and compared and integrated with one another, anda final detection result is created based on rules similar to Rules 1 to3 described in Embodiment 1.

Although the preferred embodiments of the present invention have beendescribed in detail, it should be understood that various changes,substitutions and alternations can be made therein without departingfrom spirit and scope of the inventions as defined by the appendedclaims.

Variations described for the present invention can be realized in anycombination desirable for each particular application. Thus particularlimitations, and/or embodiment enhancements described herein, which mayhave particular advantages to a particular application need not be usedfor all applications. Also, not all limitations need be implemented inmethods, systems and/or apparatus including one or more concepts of thepresent invention.

The present invention can be realized in hardware, software, or acombination of hardware and software. A visualization tool according tothe present invention can be realized in a centralized fashion in onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system—or other apparatus adapted for carrying out the methodsand/or functions described herein—is suitable. A typical combination ofhardware and software could be a general purpose computer system with acomputer program that, when being loaded and executed, controls thecomputer system such that it carries out the methods described herein.The present invention can also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which—when loaded in a computersystem—is able to carry out these methods.

Computer program means or computer program in the present contextinclude any expression, in any language, code or notation, of a set ofinstructions intended to cause a system having an information processingcapability to perform a particular function either directly or afterconversion to another language, code or notation, and/or reproduction ina different material form.

Thus the invention includes an article of manufacture which comprises acomputer usable medium having computer readable program code meansembodied therein for causing a function described above. The computerreadable program code means in the article of manufacture comprisescomputer readable program code means for causing a computer to effectthe steps of a method of this invention. Similarly, the presentinvention may be implemented as a computer program product comprising acomputer usable medium having computer readable program code meansembodied therein for causing a function described above. The computerreadable program code means in the computer program product comprisingcomputer readable program code means for causing a computer to effectone or more functions of this invention. Furthermore, the presentinvention may be implemented as a program storage device readable bymachine, tangibly embodying a program of instructions executable by themachine to perform method steps for causing one or more functions ofthis invention.

It is noted that the foregoing has outlined some of the more pertinentaspects and embodiments of the present invention. This invention may beused for many applications. Thus, although the description is made forparticular arrangements and methods, the intent and concept of theinvention is suitable and applicable to other arrangements andapplications. It will be clear to those skilled in the art thatmodifications to the disclosed embodiments can be effected withoutdeparting from the spirit and scope of the invention. The describedembodiments ought to be construed to be merely illustrative of some ofthe more prominent features and applications of the invention. Otherbeneficial results can be realized by applying the disclosed inventionin a different manner or modifying the invention in ways known to thosefamiliar with the art.

1. A digital watermark detection apparatus for detecting a digitalwatermark embedded in audio content, comprising: a plurality ofwatermark signal detection units for individually calculating, for PCMdata in the respective channels of audio content, detected values whichare correlation coefficients between frequency components of the PCMdata and pseudo random number sequences generated by a plurality of keysused to embed the digital watermark; a plurality of detected valueadding units for adding the detected values calculated by the pluralityof watermark signal detection units and corresponding to the respectivechannels and the respective keys for each possible combination of therespective channels and the respective keys; a comparison/selection unitfor receiving and comparing the respective results of the addition bythe plurality of detected value adding units with one another, andselecting and outputting one result of the addition; and a messagerestoration unit for restoring a message embedded as a digital watermarkbased on the result of the addition of the detected values, the resultbeing outputted from the comparison/selection unit, and detecting theaudio contents in which the digital watermark is embedded.
 2. Thedigital watermark detection apparatus according to claim 1, wherein, inthe plurality of detected value adding units, a detected value addingunit for outputting the detected value calculated by one of thewatermark signal detection units as is, without adding the detectedvalue to detected values calculated by the other watermark signaldetection units, is included.
 3. The digital watermark detectionapparatus according to claim 1, wherein the comparison/selection unitselects and outputs one in which a sum of absolute values of thedetected values is maximum in the received results of the addition bythe plurality of detected value adding units.
 4. The digital watermarkdetection apparatus according to claim 1, wherein thecomparison/selection unit selects and outputs one in which a sum ofsquares of the detected values is maximum in the received results of theaddition by the plurality of detected value adding units.
 5. The digitalwatermark detection apparatus according to claim 1, wherein thecomparison/selection unit performs error correction for the receivedresults of the addition by the plurality of detected value adding units,and selects and outputs one in which the number of bits, an error hasoccurred therein, is minimum.
 6. The digital watermark detectionapparatus according to claim 1, wherein the comparison/selection unitperforms error correction for the received results of the addition bythe plurality of detected value adding units, obtains correct symbols ofindividual bits to calculate signal-to-noise ratios (SNRs), and selectsand outputs one in which the obtained SNR is maximum.
 7. The digitalwatermark detection apparatus according to claim 1, wherein the messagerestoration unit is a plurality of message restoration units foraccumulating the detected values outputted from the comparison/selectionunit in accumulation cycles different from one another, restoring themessages embedded as the digital watermarks from the respectiveaccumulated detected values, and detecting the audio contents in whichthe digital watermarks are embedded, and the digital watermark detectionapparatus further comprises a detection result output unit for receivingthe respective processing results by the plurality of messagerestoration units, and synthesizing and outputting detection resultsfrom the respective processing results, for the audio contents with thedigital watermarks being embedded in the audio content.
 8. A digitalwatermark detection apparatus for detecting a digital watermark embeddedin audio content, comprising: a plurality of watermark signal detectionunits for individually calculating, for PCM data in the respectivechannels of audio content, detected values which are correlationcoefficients between frequency components of the PCM data and pseudorandom number sequences generated by a plurality of keys used to embedthe digital watermark; a plurality of detected value adding units foradding the detected values calculated by the plurality of watermarksignal detection units and corresponding to the respective channels andthe respective keys for each possible combination of the respectivechannels and the respective keys; a plurality of message restorationunits for individually receiving results of the addition by theplurality of detected value adding units, and restoring messagesembedded as the digital watermarks; and a comparison/selection unitwhich receives and compares results of restoring the messages by theplurality of message restoration units, and selecting and outputting aseries of messages.
 9. A digital watermark detection apparatus fordetecting a digital watermark embedded in audio content, comprising: awatermark signal detection unit for calculating a detected value whichis a correlation coefficient between a frequency component of PCM dataof the audio contents and a pseudo random number sequence generated by akey used to embed the digital watermark; a plurality of messagerestoration units for accumulating the detected value calculated by thewatermark signal detection unit in accumulation cycles different fromone another, restoring the message embedded as the digital watermarkfrom the accumulated detected values, and detecting the audio contentsin which the digital watermark is embedded; and a detection resultoutput unit for receiving the respective processing results by theplurality of message restoration units, and synthesizing and outputtingdetection results of the audio contents in the respective processingresults, with the digital watermarks being embedded in the audiocontent.
 10. The digital watermark detection apparatus according toclaim 9, wherein, when the audio contents in which the digital watermarkis embedded are detected by any of the message restoration units, thedetection result output unit determines that the detected audio contentsare the one in which the digital watermark is embedded, and determines aportion where the audio contents in which the digital watermark isembedded are not detected by any of the message restoration units asaudio contents in which the digital watermark is not embedded.
 11. Thedigital watermark detection apparatus according to claim 9, wherein,when the audio contents in which the digital watermarks are embedded aredetected by the plurality of message restoration units, the detectionresult output unit prioritizes a detection result by the messagerestoration unit of which accumulation cycle is shorter.
 12. The digitalwatermark detection apparatus according to claim 9, wherein, when theaudio contents in which the digital watermark is embedded is detected bya predetermined one of the message restoration units, the detectionresult output unit outputs a detection result by the message restorationunit without waiting for detections by the other message restorationunits of which accumulation cycles are longer than that of the messagerestoration unit.
 13. A digital watermark detection method for detectinga digital watermark embedded in audio contents by a computer, the methodcomprising: a first step of causing the computer to individuallycalculate, for PCM data in the respective channels of audio content,detected values which are correlation coefficients between frequencycomponents of the PCM data and pseudo random number sequences generatedby a plurality of keys used to embed the digital watermark, and to storethe calculated detected values in storing means; a second step ofcausing the computer to add the calculated detected values correspondingto the respective channels and the respective keys for each possiblecombination of the respective channels and the respective keys, and tostore the added detected values in the storing means; a third step ofcausing the computer to receive and compare the respective results ofthe addition for each combination of the respective channels and therespective keys, and to select and output one result of the addition;and a fourth step of causing the computer to restore a message embeddedas the digital watermark based on the selected and outputted result ofthe addition of the detected values, and to detect the audio contents inwhich the digital watermark is embedded.
 14. The digital watermarkdetection method according to claim 13, wherein, in the third step, onein which a sum of absolute values of the detected values is maximum inthe received results of the addition for each possible combination ofthe respective channels and the respective keys is selected andoutputted.
 15. The digital watermark detection method according to claim13, wherein, in the third step, one in which a sum of squares of thedetected values is maximum in the received results of the addition foreach possible combination of the respective channels and the respectivekeys is selected and outputted.
 16. The digital watermark detectionmethod according to claim 13, wherein, in the third step, errorcorrection is performed for the received results of the addition foreach possible combination of the respective channels and the respectivekeys, and one in which the number of bits, an error has occurredtherein, is minimum is selected and outputted.
 17. The digital watermarkdetection method according to claim 13, wherein, in the third step,error correction is performed for the received results of the additionfor each possible combination of the respective channels and therespective keys, correct symbols of individual bits are obtained tocalculate signal-to-noise ratios (SNRS), and one in which the obtainedSNR is maximum is selected and outputted.
 18. A digital watermarkdetection method for detecting a digital watermark embedded in audiocontents by a computer, the method comprising: a first step of causingthe computer to individually calculate, for PCM data in the respectivechannels of audio content, detected values which are correlationcoefficients between frequency components of the PCM data and pseudorandom number sequences generated by a plurality of keys used to embed adigital watermark, and to store the calculated detected values instoring means; a second step of causing the computer to add thecalculated detected values corresponding to the respective channels andthe respective keys for each possible combination of the respectivechannels and the respective keys, and to store the added detected valuesin the storing means; a third step of causing the computer toindividually restore messages embedded as digital watermarks based onthe respective results of the addition for each combination of therespective channels and the respective keys, and to store the restoredmessages in the storing means; and a fourth step of causing the computerto receive and compare the messages restored based on the respectiveresults of the addition with one another, and to select and output aseries of messages.
 19. A digital watermark detection method fordetecting a digital watermark embedded in audio contents by a computer,the method comprising: a first step of causing the computer to calculatea detected value which is a correlation coefficient between a frequencycomponent of PCM data of the audio contents and a pseudo random numbersequence generated by a key used to embed the digital watermark, and tostore the detected value in storing means; a second step of causing thecomputer to accumulate the calculated detected value in accumulationcycles different from one another, to restore a message embedded as thedigital watermark from the accumulated detected values, to detect theaudio contents in which the digital watermark is embedded, and to storeresults of the detection in the storing means; and a third step ofcausing the computer to receive the results of the detection based onthe plurality of accumulation cycles, and to synthesize and outputdetection results of the audio contents in the respective processingresults, with the digital watermarks being embedded in the audiocontent.
 20. The digital watermark detection method according to claim19, wherein, when the audio contents in which the digital watermark isembedded are detected by the detection using any of the accumulationcycles, in the third step, it is determined that the detected audiocontents are the one in which the digital watermark is embedded, and itis determined that a portion where the audio contents in which thedigital watermark is embedded are not detected by the detection usingany of the accumulation cycles is audio contents in which the digitalwatermark is not embedded.
 21. The digital watermark detection methodaccording to claim 19, wherein, when the audio contents in which thedigital watermarks are embedded are detected by the detections using theplurality of accumulation cycles different from one another, in thethird step, a detection result in the detection using a shorteraccumulation cycle is prioritized.
 22. The digital watermark detectionmethod according to claim 19, wherein, when the audio contents in whichthe digital watermark is embedded are detected by detection using apredetermined accumulation cycle, in the third step, a detection resultin the accumulation cycle is outputted without waiting for results ofdetections using other accumulation cycles longer than the accumulationcycle.
 23. A program for causing a computer to execute: first processingfor individually calculating, for PCM data in the respective channels ofaudio content, detected values which are correlation coefficientsbetween frequency components of the PCM data and pseudo random numbersequences generated by a plurality of keys used to embed the digitalwatermark, and for storing the calculated detected values in storingmeans; second processing for adding the calculated detected valuescorresponding to the respective channels and the respective keys foreach possible combination of the respective channels and the respectivekeys, and for storing the added detected values in the storing means;third processing for receiving and comparing the respective results ofthe addition for each combination of the respective channels and therespective keys, and for selecting and outputting one result of theaddition; and fourth processing for restoring a message embedded as thedigital watermark based on the selected and outputted result of theaddition of the detected values, and for detecting the audio contents inwhich the digital watermark is embedded.
 24. A program for causing acomputer to execute: first processing for individually calculating, forPCM data in the respective channels of audio content, detected valueswhich are correlation coefficients between frequency components of thePCM data and pseudo random number sequences generated by a plurality ofkeys used to embed a digital watermark, and for storing the calculateddetected values in storing means; second processing for adding thecalculated detected values corresponding to the respective channels andthe respective keys for each possible combination of the respectivechannels and the respective keys, and for storing the added detectedvalues in the storing means; third processing for individually restoringmessages embedded as digital watermarks based on the respective resultsof the addition for each combination of the respective channels and therespective keys, and for storing the restored messages in the storingmeans; and fourth processing for receiving and comparing the messagesrestored based on the respective results of the addition with oneanother, and for selecting and outputting a series of messages.
 25. Aprogram for causing a computer to execute: first processing forcalculating a detected value which is a correlation coefficient betweena frequency component of PCM data of audio contents and a pseudo randomnumber sequence generated by a key used to embed a digital watermark,and for storing the detected value in storing means; second processingfor accumulating the calculated detected value in accumulation cyclesdifferent from one another, for restoring a message embedded as thedigital watermark from the accumulated detected values, for detectingthe audio contents in which the digital watermark is embedded, and forstoring results of the detection in the storing means; and thirdprocessing for receiving the results of the detection based on theplurality of accumulation cycles, and for synthesizing and outputtingdetection results of the audio contents in the respective processingresults, with the digital watermarks being embedded in the audiocontent.
 26. An article of manufacture comprising a computer usablemedium having computer readable program code means embodied therein forcausing watermark detection, the computer readable program code means insaid article of manufacture comprising computer readable program codemeans for causing a computer to effect the steps of claim
 13. 27. Aprogram storage device readable by machine, tangibly embodying a programof instructions executable by the machine to perform method steps forwatermark detection, said method steps comprising the steps of claim 18.